JP2010256205A - Range finding device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a range finding device capable of performing preliminary measurement properly, even if the S/N ratio is poor. <P>SOLUTION: This range finding device includes a light transmission means 4 for transmitting light toward an object; a light-receiving means 5 for receiving light reflected by the object; calculating means 1, 2 for operating a distance to the object based on a time from transmission of light until reception of the light; and a control means 1 for controlling the light transmission means 4, the light-receiving means 5 and the calculating means 1, 2 respectively so as to perform preliminary measurement before main measurement, and to perform main measurements by using a preliminary measurement value. The control means 1 at the preliminary measurement time controls repeated transmissions of the light, reception of the light, and the calculating so that a distance calculating value is operated as many as a prescribed number of times by the calculating means 1, 2; determines a histogram based on a plurality of distance calculating values acquired by calculating for the prescribed number of times; and when the maximum frequency among the frequencies in the histogram is equal to or higher than a first determination threshold P1, acquires the preliminary measured value, by using the distance calculating value included in the class of the maximum frequency. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a distance measuring device.

  In a distance measuring device that measures the distance to an object based on the time difference between the time when light is transmitted toward the object and the time when reflected light from the object is received, a preliminary measurement is performed before the main measurement. A technique for measuring an approximate distance to an object by performing is known (see Patent Document 1).

JP 2003-255046 A

  In the prior art, when the distance to the object is far away or the reflectance of the object is low and the reflected light is weak, the S / N ratio is lowered, and it is easily affected by noise in the preliminary measurement. There was a problem.

  The present invention calculates a distance to an object based on a light transmission means for transmitting light toward the object, a light receiving means for receiving light reflected by the object, and a time from light transmission to light reception. A distance measuring apparatus comprising: a calculating means for performing a preliminary measurement before the main measurement, and a control means for controlling the light transmitting means, the light receiving means and the calculating means so as to perform the main measurement using the preliminary measurement value. Applied. The control means at the time of preliminary measurement repeatedly controls light transmission, light reception and calculation so that the calculation means calculates the distance calculation value a predetermined number of times, and based on a plurality of distance calculation values obtained by calculating the predetermined number of times. A histogram is obtained, and when the maximum frequency among the frequencies of the histogram is equal to or greater than the first determination threshold value P1, a preliminary measurement value is obtained using a distance calculation value included in the class of the maximum frequency.

  In the distance measuring apparatus according to the present invention, it is possible to appropriately perform preliminary measurement even if the S / N ratio is poor.

1 is a block diagram illustrating an electrical configuration of a lightwave distance measuring device according to an embodiment of the present invention. It is a block diagram explaining the optical structure of the light wave type distance measuring apparatus of FIG. It is a flowchart explaining the flow of the preliminary measurement process performed with a calculation control circuit. It is a flowchart explaining the flow of the preliminary measurement process performed with a calculation control circuit.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a block diagram for explaining the electrical configuration of a lightwave distance measuring device according to an embodiment of the present invention. In FIG. 1, the distance measuring apparatus includes an arithmetic control circuit 1, a time measurement circuit 2, a drive circuit 3, a light transmission circuit 4, a light reception circuit 5, an amplification circuit 6, a timing detection circuit 7, a signal level. It has a measurement circuit 8 and a dimming filter unit 9.

  The arithmetic control circuit 1 is constituted by a microcomputer or the like, and controls the operation of each part in the distance measuring device and detects the level of the received signal 1 described later. The time measuring circuit 2 is configured by an FPGA (Field Programmable Gate Array) or the like. The time measurement circuit 2 sends a transmission trigger signal S102 to the drive circuit 3 in response to the measurement start signal S101 sent from the arithmetic control circuit 1. The time measurement circuit 2 further measures a time t from when the transmission trigger signal S102 is transmitted until a measurement stop signal S112 described later is received. Here, the time t is the time from when the external light transmission pulse 105 is transmitted toward the object through the light transmission optical system 42 described later until the light reception pulse 106 is received through the light reception optical system 51. Correspondingly, the propagation delay time of each circuit is adjusted in advance.

  The arithmetic control circuit 1 calculates the product of the time t and the speed of light to obtain the distance D to the object. Specifically, it is calculated by D = c / n × t / 2. Here, c is the speed of light in vacuum, and n is the refractive index of air. The reason why c is divided by n is to obtain the speed of light in the air because the external light transmission pulse 105 and the light reception pulse 106 travel in the air. Further, the reason for dividing by 2 is that the time t corresponds to the round-trip time of light between the object and the distance measuring device, so that it is converted into a one-way distance.

  The drive circuit 3 sends a transmission drive signal S103 synchronized with the transmission trigger signal S102 to the light transmission circuit 4. The light transmission circuit 4 includes a light emitting element 41 and a light transmission optical system 42. The light transmission circuit 4 pulse-drives the light emitting element 41 according to the transmission drive signal S103 and outputs the light emission pulse 104. The light emitting element 41 is configured by, for example, a laser diode that emits light having an infrared wavelength.

  When the internal optical path switch 42-c (described later with reference to FIG. 2) is switched to the “internal optical path” side, the light transmission optical system 42 performs light control using the light transmission pulse 104 as the internal light transmission pulse 115. Guide to the filter unit 9. The dimming filter unit 9 outputs an internal light reception pulse 116 in which the internal light transmission pulse 115 is attenuated to a predetermined signal level.

  On the other hand, the light transmission optical system 42 when the internal optical path switch 42-c is switched to the “external optical path” side transmits the light transmission pulse 104 toward the object as the external light transmission pulse 105. The object is, for example, a surveying target. The optical path switch 42-c is controlled by an optical path switching signal S117 sent from the arithmetic control circuit 1.

  The reflected light from the object is received by the light receiving circuit 5 as a light receiving pulse 106. The light receiving circuit 5 includes a light receiving optical system 51, a dimming circuit 52, a multiplexing circuit 53, and a light receiving element 54. The received light pulse 107 that has passed through the light receiving optical system 51 enters the light receiving element 54 via the dimming circuit 52 and the multiplexing circuit 53. The dimming circuit 52 has, for example, a density variable filter driven by a motor (not shown), attenuates the light reception pulse 106, and outputs a light reception pulse 108 of a predetermined level. The amount of light attenuation by the light control circuit 52 is controlled by a motor drive signal S118 sent from the arithmetic control circuit 1.

  When the above-described internal light reception pulse 116 is incident, the multiplexing circuit 53 guides the light reception pulse to the light receiving element 54 as reception pulse light 109. Further, when the light reception pulse 108 described above is incident, the multiplexing circuit 53 guides the light reception pulse to the light receiving element 54 as the reception pulse light 109.

  The light receiving element 54 is composed of, for example, an avalanche photodiode, and photoelectrically converts the received pulsed light 109. The photoelectric conversion signal is sent to the amplifier circuit 6 as a reception signal S110. The amplification circuit 6 amplifies the reception signal S110 and sends the amplified reception signal S111 to the timing detection circuit 7 and the signal level measurement circuit 8, respectively.

  The timing detection circuit 7 detects a timing at which the level of the reception signal S111 reaches a peak, and sends a measurement stop signal S112 corresponding to the peak timing to the time measurement circuit 2. Upon receiving the measurement stop signal S112, the time measurement circuit 2 sends a measurement end signal S114 to the arithmetic control circuit 1.

  Upon receiving the reception signal S111, the signal level measurement circuit 8 sends an amplitude level signal S113 corresponding to the peak level of the reception signal S111 to the arithmetic control circuit 1. The arithmetic control circuit 1 detects the level of the signal S113 by A / D converting the amplitude level signal S113 with a built-in A / D converter (not shown) using the measurement end signal S114 as a trigger.

  FIG. 2 is a block diagram illustrating an optical configuration of the light wave type distance measuring apparatus of FIG. In FIG. 2, the optical system of the distance measuring device is roughly divided into a light transmitter 4 </ b> A, a light receiver 5 </ b> A, and a telescope unit 10. In the present embodiment, the optical axes of the light transmitting unit 4A, the light receiving unit 5A, and the telescope unit 10 are configured on the same axis, and a part of the configuration such as an objective lens described later is provided between the light transmitting unit 4A, the light receiving unit 5A, and the telescope unit 10. It is also used in.

  The light transmitting unit 4A includes a light emitting element 41 and a light transmitting optical system 42. The light transmission optical system 42 includes a lens 42-a, a beam splitter 42-b, an optical path switch 42-c, a mirror 42-d, and an objective lens 42-e. The lens 42-a collimates the light emitted from the light emitting element 41. The beam splitter 42-b divides the incident light into two. The optical path switch 42-c that has received the switching instruction to the “internal optical path” side by the optical path switching signal S117 (FIG. 1) guides the light emitted from the beam splitter 42-b to the dimming filter unit 9. Further, the optical path switch 42-c that has received an instruction to switch to the “external optical path” by the optical path switching signal S117 (FIG. 1) guides the light emitted from the beam splitter 42-b to the mirror 42-d.

  The mirror 42-d bends the light emitted from the beam splitter 42-b (referred to as distance measuring light) and guides it to the objective lens 42-e. The objective lens 42-e emits distance measuring light toward the object. In the present embodiment, the distance measuring light is emitted through the central portion of the objective lens 42-e when switching to the “external optical path” side. As described above, the objective lens 42-e is configured to serve as the objective lens 10-a of the telescope unit 10 and the objective lens 51-a of the light receiving unit 5A.

  The light receiving unit 5A includes a light receiving optical system 51, a light adjusting unit 52, a multiplexing unit 53A, and a light receiving element 54. The light receiving optical system 51 includes an objective lens 51-a and a dichroic prism 51-b. Light from the object incident on the objective lens 51-a is guided to the dichroic prism 51-b. The dichroic prism 51-b bends light of a predetermined wavelength component (in this embodiment, the infrared wavelength region) and guides it to the coupling prism 53-a, and transmits light other than the predetermined wavelength component (visible wavelength region light in this embodiment). Guide to the observation optical system of the telescope unit 10.

  The dimming unit 52 corresponds to the dimming circuit 52 of FIG. The multiplexing unit 53A corresponds to the multiplexing circuit 53 of FIG. 1, and includes a coupling prism 53-a, a receiving fiber 53-b, and a coupling optical system 53-c. The coupling prism 53-a causes the light attenuated by the dimming filter unit 9 to enter the reception fiber 53-b, while the light (infrared wavelength light) bent by the dichroic prism 51-b is received by the reception fiber 53-b. To enter. The light passing through the receiving fiber 53-b is incident on the light receiving surface of the light receiving element 54 by the coupling optical system 53-c. Here, the coupling optical system 53-c includes a wavelength selection filter, and is configured to attenuate unnecessary light (for example, sunlight) having a wavelength different from the emission wavelength (infrared wavelength) by the light transmitting unit 4A. .

  The telescope unit 10 includes an objective lens 10-a (also used as 51-a and 42-e), a dichroic prism 10-b (also used as 51-b), and an observation optical system. The observation optical system includes, for example, a focusing lens 10-c, an erecting prism 10-d, a focusing screen 10-e, and an eyepiece lens 10-f.

  The visible light guided to the observation optical system forms an image on the focusing screen 10-e through the focusing lens 10-c and the erecting prism 10-d. The observer observes the intermediate erect image on the focusing screen 10-e through the eyepiece 10-f.

The distance measuring device performs distance measurement processing from the distance measuring device to the object in the order of (i) light quantity balance processing, (ii) preliminary measurement processing, and (iii) main measurement processing.
<Light balance processing>
The light quantity balancing process includes the light receiving level of the light received by the light receiving unit 5A when switching to the “internal optical path” and the light receiving of the light received by the light receiving unit 5A when switching to the “external optical path”. This is a process of adjusting the attenuation amount by the dimming unit 52 so as to align the level. Specifically, the level of the signal S113 detected by the arithmetic control circuit 1 when switching to the “external optical path” side is brought closer to the level of the signal S113 detected by the arithmetic control circuit 1 when switching to the “internal optical path” side. The light reception level is adjusted by changing the motor drive signal S118 sent to the light control unit 52.

<Preliminary measurement processing>
The preliminary measurement process is a process in which an approximate distance from the distance measuring device to the object is measured before this measurement, and this approximate distance is set as a preliminary measurement value DP. Details of the preliminary measurement process will be described later.

<Main measurement process>
In this measurement process, the distance from the distance measuring device to the object is repeatedly measured a predetermined number of times using the preliminary measurement value DP. Of the measurement values, the measurement values outside the predetermined range including the preliminary measurement value DP are discarded, and the measurement values are included in the predetermined range until the number of measurement values included in the predetermined range reaches a preset number of measurements (for example, 2000 to 7000 times). Repeat the measurement. The distance measuring device obtains the distance D (main measured value) to the object by, for example, calculating a simple average value based on the measured values for the predetermined number of times.

  Since the present embodiment has a feature in the preliminary measurement process, the following description will focus on the preliminary measurement process with reference to a flowchart. 3 and 4 are flowcharts illustrating the flow of the preliminary measurement process. The arithmetic control circuit 1 causes the time measurement circuit 2 to perform a preliminary measurement process following the light intensity balancing process of (i).

  In step P1 of FIG. 3, the time measurement circuit 2 initializes (resets here) the preliminary measurement count c, the approximate distance integrated value Sdp, and the effective approximate distance data number Ndp, and proceeds to step P2. In the present embodiment, when a predetermined number of approximate distances obtained by a predetermined number of distance measurements performed in the preliminary measurement have a predetermined unitary state, these approximate distances are adopted as effective approximate distances. On the other hand, if it does not have a predetermined unity state, a preliminary measurement is newly performed. In this example, for example, a histogram of the 30 approximate distances is obtained by setting 30 distance measurements as one set, and when the maximum frequency of the histogram is less than a predetermined value (for example, 15), another set (30 times) Preliminary measurement is performed for up to 20 sets.

  The preliminary measurement count c is used as a counter for counting the number of sets. The approximate distance integrated value Sdp represents an integrated distance obtained by integrating the effective approximate distance. The effective approximate distance data number Ndp represents the number of the effective approximate distances.

  In step P2, the time measuring circuit 2 performs a preliminary measurement for one set, and stores the approximate distance data D1 to Dn (n = 30 in this example) at addresses A1 to An (n = 30) of the memory, respectively. Further, the approximate distance data D1 to Dn are sequentially associated with the distance integrated value data S1 to Sk, and F1 to Fn corresponding to the addresses A1 to An are initialized (reset here), and the process proceeds to Step P3. F1 to Fn are used as counters for counting the frequencies in the histogram.

  Further, the arithmetic control circuit 1 increases the value of the number of times of measurement n per set when the level of the signal S113 detected in the state of switching to the “external optical path” side at the time of the light quantity balancing process described above is lower than a predetermined level. In this embodiment, normally n = 30 preliminary measurements are set as one set. However, when the level of the signal S113 is low, for example, the number is changed to increase n = 60. As a result, in a situation that is easily affected by noise, distance measurement twice as normal is performed, and 60 approximate distances per set are obtained.

  In step P3, the time measuring circuit 2 sets the initial value 1 to the address max storing the maximum frequency Fmax and the initial value 1 to the maximum frequency Fmax, and proceeds to step P4. The time measurement circuit 2 initializes the initial approximate distance data (D1) stored at the address A1.

  In Step P4, the time measuring circuit 2 reads the second and subsequent approximate distance data Dk stored in the addresses A2 to An, and proceeds to Step P5. In step P5, the time measuring circuit 2 compares the approximate distance data Dk for the second and subsequent times with the data D (k-1) having a younger address, and proceeds to step P6.

  In Step P6, the time measuring circuit 2 determines whether or not the difference in the approximate distance data is within a predetermined range. If the difference in the approximate distance data is within the predetermined range, the time measuring circuit 2 makes a positive determination in step P6 and proceeds to step P10. If the difference in the approximate distance data is outside the predetermined range, the time measuring circuit 2 makes a negative determination in step P6 and proceeds to step P7.

  In step P7, the time measuring circuit 2 adds +1 to the frequency counter Fk corresponding to the address Ak, and proceeds to step P8. As a result, when the approximate distance data Dk is not substantially coincident with all of the approximate distance data D1 to D (k-1), the address Ak is incremented by one in the next step P8 in order to change the comparison target.

  In Step P8, the time measuring circuit 2 adds +1 to the address Ak and proceeds to Step P9. In step P9, the time measuring circuit 2 determines whether or not k> n is satisfied (that is, whether or not the approximate distance data Dk at the address Ak is the 30th data in one set). The time measurement circuit 2 makes a positive determination in step P9 when k> n is satisfied, and proceeds to step P14 in FIG. If k> n is not satisfied, the time measuring circuit 2 makes a negative determination in step P9 and returns to step P4. When returning to Step P4, the comparison process described above is repeated.

  In step P10, which proceeds after making an affirmative determination in step P6 described above, the time measurement circuit 2 adds +1 to the frequency counter Fi corresponding to the younger address Ai of the approximate distance data that are substantially matched, and adds to the distance integrated value data Si. The approximate distance data Dk is added, and the process proceeds to Step P11.

  In Step P11, the time measuring circuit 2 determines whether or not “i” of the substantially matched younger address matches the address max. If “i” matches the address max at which the maximum frequency is stored, the time measurement circuit 2 makes an affirmative decision in step P11 and proceeds to step P8. If “i” does not match the address max, the time measurement circuit 2 makes a negative determination in step P11 and proceeds to step P12.

  In Step P12, the time measuring circuit 2 determines whether or not the frequency counter Fi is larger than the maximum frequency Fmax. If Fi> Fmax is established, the time measuring circuit 2 makes a positive determination in step P12 and proceeds to step P13. If Fi> Fmax is not satisfied, the time measuring circuit 2 makes a negative determination in step P12 and proceeds to step P8.

  In step P13, the time measuring circuit 2 changes the address “i” to the address max. As a result, the integrated value Si of the approximate distance data included in the class corresponding to the frequency counter Fi becomes the integrated value Smax of the approximate distance value included in the class of the maximum frequency Fmax.

  The process of steps P4-P13 described above corresponds to the creation of a histogram for obtaining the frequency for each class for 30 approximate distance data. In the present embodiment, it is sufficient that the maximum frequency and the approximate distance data corresponding to the maximum frequency can be specified, so that the processing for charting is not necessary.

  In step P14 of FIG. 4, the time measuring circuit 2 determines whether or not the maximum frequency Fmax is equal to or greater than a predetermined number (15 in this example). When the maximum frequency Fmax is 15 or more, the time measuring circuit 2 makes an affirmative decision in step P14 and proceeds to step P15. If the maximum frequency Fmax is less than 15, the time measuring circuit 2 makes a negative determination in step P14 and proceeds to step P16.

  When proceeding to Step P15, the preliminary measurement process is terminated. In step P15, the time measuring circuit 2 sets the quotient obtained by dividing the approximate distance integrated value Smax by the maximum frequency Fmax as the approximate distance by the preliminary measurement process. That is, the preliminary measurement process is terminated with the average value of the approximate distance data included in the class of the maximum frequency as the preliminary measurement value DP.

  In Step P16, the time measuring circuit 2 determines whether or not the number of preliminary measurements c is 1. When c = 1 (that is, the first set in the preliminary measurement), time measurement circuit 2 makes an affirmative decision in step P16 and proceeds to step P17. The time measurement circuit 2 makes a negative determination in step P16 when c ≠ 1 (that is, the second and subsequent sets in the preliminary measurement), and proceeds to step P18.

  In step P17, the time measurement circuit 2 stores the quotient (first set preliminary measurement value DP1) obtained by dividing the approximate distance integrated value Smax by the maximum frequency Fmax in the memory as the approximate distance integrated value Sdp. Proceed to P24. As a result, the average value of the approximate distance data included in the maximum frequency class of the histogram based on the first set of preliminary measurement values becomes the approximate distance integrated value Sdp.

  In Step P18, the time measurement circuit 2 calculates a quotient (preliminary measurement value DPc of the c-th set (c ≧ 2)) obtained by dividing the approximate distance integrated value Smax by the maximum frequency Fmax, and proceeds to Step P19. Thus, the average value of the approximate distance data included in the class of the maximum frequency of the histogram based on the c-th preliminary measurement value becomes the c-th preliminary measurement value DPc.

  In Step P19, the time measuring circuit 2 determines whether or not | DPc−DP1 | ≦ specified value is satisfied. When the difference between the c-th preliminary measurement value DPc and the first set preliminary measurement value DP1 is within a predetermined value, the time measurement circuit 2 makes an affirmative decision in step P19 and proceeds to step P20. If the difference between the c-th preliminary measurement value DPc and the first set preliminary measurement value DP1 exceeds a predetermined value, the time measurement circuit 2 makes a negative determination in step P19 and proceeds to step P24. When negative determination is made in step P19, the preliminary measurement value DPc is not adopted as the effective approximate distance.

  When proceeding to Step P20, the preliminary measurement value DPc is adopted as the effective approximate distance. In Step P20, the time measurement circuit 2 integrates the c-th preliminary measurement value DPc with the approximate distance integration value Sdp and proceeds to Step P21.

  In step P21, the time measuring circuit 2 adds +1 to the effective approximate distance data number Ndp and proceeds to step P22. In Step P22, the time measuring circuit 2 determines whether or not the effective approximate distance data number Ndp has reached a specified number. The time measuring circuit 2 makes an affirmative decision in step P22 when Ndp = a prescribed number (for example, 10) and proceeds to step P23. The time measuring circuit 2 makes a negative determination in step P22 when Ndp ≠ a prescribed number (for example, 10), and proceeds to step P24.

  In step P24, the time measuring circuit 2 adds +1 to the number of preliminary measurements c, and proceeds to step P25. In Step P25, the time measuring circuit 2 determines whether or not the number of preliminary measurements c is equal to or less than a specified number. The time measurement circuit 2 makes an affirmative decision in step P25 when c is a predetermined number (for example, 20) or less, and returns to step P2 in FIG. 3 to perform the next set of preliminary measurements. On the other hand, the time measurement circuit 2 makes a negative determination in step P25 when c exceeds a predetermined number (20) (that is, the distance measurement for 20 sets has been completed), and proceeds to step P26.

  In step P26, the time measuring circuit 2 outputs an error indicating that the preliminary measurement has not been performed normally, and ends the preliminary measurement process. Error output is performed, for example, by turning on an alarm lamp (not shown) or generating an alarm sound from a speaker (not shown).

  In Step P23, the time measuring circuit 2 sets the quotient obtained by dividing the approximate distance integrated value Sdp by the effective approximate distance data number Ndp as the approximate distance by the preliminary measurement process. That is, the preliminary measurement process is terminated with the average value of the adopted preliminary measurement values DPc as the preliminary measurement value DP.

  The time measurement circuit 2 after the preliminary measurement process enters the main measurement process when the preliminary measurement value DP is obtained in step P15 or step P23 (that is, when the preliminary measurement process is normally completed). When the preliminary measurement error is output by finishing the preliminary measurement process, the time measuring circuit 2 performs the light quantity balancing process again without proceeding to the main measurement process.

  In the main measurement process, the main measurement values included in a predetermined range with respect to the preliminary measurement value DP among the plurality of main measurement values to be calculated until the number of measurement reaches the above-mentioned number of measurements (for example, 2000 to 7000 times). Repeat the measurement. Here, the “predetermined range” in the main measurement is made wider than the “predetermined range” determined by the predetermined value used for the determination in step P19 in the preliminary measurement process. For example, in the preliminary measurement process (step P19), when it is determined whether the difference between the preliminary measurement value DPc and the first set preliminary measurement value DP1 is within ± 0.4 m, It is determined whether or not the difference between the measured value DP and the actual measured value is within ± 0.6 m. Then, the main measurement value deviating from ± 0.6 m with respect to the preliminary measurement value DP is discarded, and the number of the main measurement values included in the preliminary measurement value DP ± 0.6 m is the above-mentioned number of measurements (for example, 2000 to 7000 times). Repeat this measurement until

  When the time measurement circuit 2 finishes the number of times of the main measurement, the time measurement circuit 2 sends a measurement end signal S114 to the calculation control circuit 1, and the calculation control circuit 1 obtains an integrated value of time data corresponding to the number of times of the main measurement from the time measurement circuit 2. receive. The arithmetic control circuit 1 calculates, for example, a simple average value from the received integrated value, and further calculates the distance D to the object by performing an operation including the above-mentioned light speed and refractive index.

According to the embodiment described above, the following operational effects can be obtained.
(1) An operation for performing a preliminary measurement before the main measurement and calculating the distance by controlling the light transmitting circuit 4 and the light receiving circuit 5 so as to perform the main measurement using the preliminary measurement value DP (rough distance). The control circuit 1 and the time measurement circuit 2 repeatedly control light transmission, light reception and calculation so that the distance calculation value is calculated a predetermined number of times during preliminary measurement, and a plurality of distance calculation values obtained by calculating the predetermined number of times. The maximum frequency Fmax is greater than or equal to a predetermined value P1 (for example, 15) among the frequencies of the histogram, and the preliminary measurement value DP is obtained using the distance calculation value included in the class of the maximum frequency Fmax. did. Thereby, preliminary measurement can be appropriately performed even in a state where the S / N ratio is poor.

(2) When the number of distance calculation values to be calculated reaches N (for example, 30), the time measuring circuit 2 in (1) obtains a histogram relating to the 30 distance calculation values, and out of the frequency of the histogram When the maximum frequency is less than P1 (for example, 15), the light transmission, light reception, and calculation are repeatedly controlled so that 30 distance calculation values are calculated. By limiting the number of measurements per set to 30, the amount of memory used is reduced and the processing burden is reduced, compared to the case where the number of measurements is unlimited, and the scale of the circuit used for computation (for example, the number of gates of FPGA) Can be suppressed.

(3) The time measurement circuit 2 of (2) obtains a class having the maximum frequency for each histogram related to the 30 distance calculation values, and calculates the distance calculation value included in the maximum class for each maximum class. An average value (referred to as a distance average value) is obtained, and the number of distance average values included in the first predetermined range X1 (for example, ± 0.4 m) among the distance average values for each maximum class is a predetermined value P2 (for example, 10). ) In the above case, the preliminary measurement value DP is obtained using the distance average value included in X1. As a result, only the distance calculation value having a predetermined unitary state is employed to obtain the preliminary measurement value DP, and therefore, the distance calculation value having a large variation (ie, no unity) due to the influence of noise or the like is excluded. be able to.

(4) The time measurement circuit 2 of (3) above has the number of distance average values included in X1 less than P2 (for example, 10) even if the calculation of the 30 distance calculation values is repeated M (for example, 20) times. In this case, since the preliminary measurement value DP is not obtained, it is possible to prevent the useless preliminary measurement from being continued when the variation is large due to the influence of noise or the like (that is, there is no unity).

(5) The arithmetic control circuit 1 increases the value of N from the normal value of 30 to 60 when the reflected light level received by the light receiving circuit 5 is lower than the predetermined level. It is possible to increase the possibility that a preliminary measurement value can be obtained while the variation is large as compared to the case where there is no variation.

(6) The time measuring circuit 2 of (1) to (5) performs light transmission, light reception and calculation so as to calculate a distance calculation value for a predetermined number of main measurements (for example, 2000 to 7000) at the time of main measurement. By repeatedly controlling, the main measurement value is obtained by using the distance calculation value within the second predetermined range X2 (for example, ± 0.6 m) including the preliminary measurement value DP among the distance calculation values of a predetermined number of main measurements. Therefore, for example, an abnormal distance calculation value (a value greatly different from the preliminary measurement value DP) obtained when a person, a car, an animal, or the like crosses between the distance measuring device and the object during the main measurement can be eliminated.

(7) The time measurement circuit 2 of (6) described above has a third predetermined number Q (2000 to 2000) in which the number of distance calculation values in X2 (for example, ± 0.6 m) is greater than (N × M) during the main measurement. Since the main measurement is continued until 7000), the influence of noise can be kept low.

(8) Since the time measuring circuit 2 in (6) or (7) described above has X2 wider than X1, the time required for this measurement processing is shortened compared to the reverse case (X2 is narrower than X1). Can do.

(Modification 1)
In step P15 in FIG. 4, instead of using the average value of all the approximate distance data included in the maximum frequency class as the preliminary measurement value DP, the average value of a part of the approximate distance data included in the maximum frequency class is reserved. The measured value DP may be used. For example, the maximum value and the minimum value of the approximate distance data included in the maximum frequency class are excluded, and the average value of the remaining approximate distance data is set as the preliminary measurement value DP. Note that the same applies to the case where the c-th preliminary measurement value DPc is calculated (step P17, step P18).

(Modification 2)
Moreover, although the example which calculates a simple average and obtains a preliminary measurement value was demonstrated in step P15, P17, and P18 mentioned above, you may obtain a preliminary measurement value by performing a weighting process instead of a simple average.

(Modification 3)
In the above embodiment, when the c-th preliminary measurement value DPc is within a predetermined difference from the first set preliminary measurement value DP1 in step P19 in FIG. 4, the preliminary measurement value DPc is adopted as the effective approximate distance. . Instead, out of 20 sets of preliminary measurement values DPx (1 ≦ x ≦ 20), 10 preliminary measurement values DPxi with small variations (corresponding to the prescribed number in step P22) are extracted and used as effective approximate distances. You may make it do.

  The above description is merely an example, and is not limited to the configuration of the above embodiment. The threshold value and the number of times used for each determination may be changed as appropriate.

DESCRIPTION OF SYMBOLS 1 ... Operation control circuit 2 ... Time measurement circuit 3 ... Drive circuit 4 ... Light transmission circuit 5 ... Light reception circuit 6 ... Amplification circuit 7 ... Timing detection circuit 8 ... Signal level measurement circuit 9 ... Dimming filter part

Claims (8)

A light transmission means for transmitting light toward the object;
A light receiving means for receiving the light reflected by the object;
A calculation means for calculating a distance to the object based on a time from the light transmission to the light reception;
Preliminary measurement is performed prior to the main measurement, and the light transmitting means, the light receiving means, and the calculation means are respectively controlled so as to perform the main measurement using the preliminary measurement value.
The control means at the time of the preliminary measurement is
Repetitively controlling the light transmission, the light reception and the calculation so as to calculate a distance calculation value a predetermined number of times by the calculation means;
Obtain a histogram based on a plurality of distance calculation values obtained by calculating the predetermined number of times,
When the maximum frequency among the frequencies of the histogram is equal to or greater than a first determination threshold value P1, the distance measurement device obtains the preliminary measurement value using a distance calculation value included in the class of the maximum frequency. The distance measuring device according to claim 1,
The control means at the time of the preliminary measurement is
When the number of distance calculation values calculated by the calculation means reaches the first predetermined number N, a histogram relating to the N distance calculation values is obtained,
A distance measuring apparatus that repeatedly controls the light transmission, the light reception, and the calculation so as to calculate N distance calculation values when the maximum frequency in the histogram is less than P1. The distance measuring device according to claim 2,
The control means at the time of the preliminary measurement is
For each of the histograms related to the N distance calculation values, obtain a class having the maximum frequency,
For each maximum class, find the average value of the distance calculation values included in the maximum class (referred to as the distance average value)
When the number of distance average values included in the first predetermined range X1 among the distance average values for each maximum class is equal to or greater than the second determination threshold value P2, the distance average value included in the X1 is used to A distance measuring device characterized by obtaining preliminary measurement values. In the distance measuring device according to claim 3,
The control means at the time of the preliminary measurement is
If the number of distance average values included in the X1 is less than the P2 even if the calculation of the N distance calculation values is repeated a second predetermined number M times, the preliminary measurement value acquisition is stopped. Ranging device. In the distance measuring device according to any one of claims 2 to 4,
The control means at the time of the preliminary measurement is
The distance measuring apparatus, wherein the first predetermined number N is increased when a reflected light level received by the light receiving means is lower than a predetermined level. In the distance measuring device according to any one of claims 1 to 5,
The control means at the time of the main measurement is
Repetitively controlling the light transmission, the light reception and the calculation so as to calculate a distance calculation value of a predetermined number of times of main measurement by the calculation means;
A distance measuring apparatus that obtains the main measurement value using a distance calculation value within a second predetermined range X2 including the preliminary measurement value among the distance calculation values of the predetermined number of main measurements. The distance measuring device according to claim 6,
The control means at the time of the main measurement is
The distance measuring apparatus according to claim 1, wherein the main measurement is continued until the number of distance calculation values in X2 reaches a third predetermined number Q that is greater than (N × M). The distance measuring device according to claim 6 or 7,
The distance measuring apparatus characterized in that the control means at the time of the main measurement makes the X2 wider than the X1.

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